Dear Mr. Morrish,

1.0) Please inform the belt width, belt speed, material name, material size gradation and tripper inclination for more meaningful reply.

2.0) General solutions are :

2.1) Ensure continuity of flow.

2.2) Use the heavier belt i.e. when you are replacing the belt, opt for the same carcass but with thicker covers. This is a design analysis issue.

2.3) Use of hold down discs on curvature. This minimizes the spillage but does not eliminate the spillage.

2.4) Make the conveyor starting more smooth / gradual, this will enable to reduce the dead tension in the belt and thereby minimize the chances of lift up. This is design analysis issue.

2.5) Modify the tripper zone i.e. make it longer, but this is a major work.

2.6) Review the type of drive/s for minimum tension in the belt.

Regards,

Ishwar G Mulani.

Author of Book : Engineering Science and Application Design for Belt Conveyors.

Advisor / Consultant for Bulk Material Handling System & Issues.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 25882916 ■

Hello Again James,

Spillage can be minimized using curved chutes engineered for the installation.

As much as is written on how to control product flow in transfers, it is still a hard sell for some. Wait one year from now and see the numbers increase around the world. the testimonials such as tripper/stackers will hard to ignore.

LKN ■

A specific point on rollback and bad transfer designs:

Flow onto incline stackers is usually through a direct drop. Product hits the belt, from the verticalk fall, with a reverse vector to belt and product flow direction. Rock rotation is initiated as the rock is accelerated to belt velocity. Without adjacent interlocking rocks, the rock can begin to tumble and bounce backward. Spin momentum is increased and rock careens out of control. Belt wear and gouging damage and product spillage are dominant.

Proper chute design brings the rock onto the belt at near belt speed and in the same direction as belt travel. There can be instable instances of the above adverse phenomena, but they are reduced by many multiples. Try it. We guaranty it or no pay.

Lawrence Nordell

Conveyor Dynamics, Inc.

www.conveyor-dynamics.com ■

James:

Garabe in yields garbage out. There is a difference in curved chute technology - those with physics and those that suck-it-and-see. We have curved chutes working in clay. Liner materials, their surface finish selection and idealized chute geometry differ between designers. DEM allows material rheology sensitivity analysis to optimized curved shape and liner materials to the variances of product flow properties.

Are you running all clay at times? Western Australia Yandi iron ores have extreme wet fines and large lump clay lenses. The curved hood and spoons are working. There have been hicups with Dua plate and its very poor surface finish and flow interrupting shapes. Design shapes submitted get altered by commitees.

Would you like to have your failed chute evaluated against our alternative?

It is a shame you get the bad apple that spoils the barrel - ancient ineffective engineering tools. We have also learned that too many cooks spoil the broth - optimal design is altered by others.

I can say the same about tripper designs. Designs become compromised in the details:

1. biggest drop in higher tension comes with better rolling efficient rubber

2. use dual drive with best power ratio to minimize counterweight

3. use ceramic lagged drive pulleys to minimiize counterweight

4. place counterweight at tail pulley also requiring optimum soft-start to control belt tension to necessary belt sag level

5. larger idler diameter rolls to bring belt tension & power down

6. idler support optimized to extend belt support at base of curve on moving tripper frame

7. belts wear less with a proper chute design

8. optimized belt speed and width to select best fit for tension in concave curve and total cost of ownership

9. give Dave Beckeley a shout - one of the belt tripper designers in OZ.

All engineers do not produce the same solution. However, they do tend to copy once the working model is known.

Please forgive bad spelling, grammar and punctuations.

Regards,

Lawrence Nordell

Conveyor Dynamics, Inc.

www.conveyor-dynamics.com ■

James,

Based on some of the replies, I am not sure if your concern is loading points & chutes or mainly the section up the inclines & on the curve. If it is the latter, I have installed several full, non-contact skirt installations and have recently seen the proporitary plastic belt covers used for this same problem. Any permanent skirts become a problem for idler replacement, so swing-up ones may be necessary. Also have a good look at what caused the lead-in & tail-out 'dribbles'. There is often something which can be done to reduce these significantly (feeder starting, clamshell door opening, belt sequencing etc.). For the belt-lift problem VF drives which give slow starts and reduce/eliminate belt lift problems on startup but won't help if belt lifts off on normal running when flow stops (shouldn't normally happen). I realise the roll-back spillage can happen at any time - even with belt not lifting - so full length skirts & covers may be your best solution. Have a look at the light, relatively inexpensive plastic ones. When the lumps are large the lump rollback can also become a safety issue for people on the walkways. ■

Dear Mr. James Morrish,

The proper radius at tripper zone is a critical issue. There are generally established practices.

1) If we use radius, as calculated for fixed conveyor zone, the radius and thereby the tripper length will be large. This is maximum tension and as if belt is empty only at curvature. As said before, this will lead longer tripper and hence expensive machine.

2) As the people want to economize tripper connected with stacker or stacker cum reclaimer machine, they design as per serial no. 1 but with 20% material load. This is just a compromise and it will work most of the time, because the worst situation which is being considered in serial no. 1 rarely happens (such as starting tension and belt is empty only at curvature, etc). This method is commonly used by reputed designer / manufacturer of the mobile machine, and so it is understood that it will rarely give trouble.

As far as belt lift is concerned, it is simply related to belt tension, belt mass kg/m, and earth’s gravity pull. So, only way to prevent this is to either reduce the tension or increase the mass (as we cannot do anything about earth’s gravity). So, I suggest you to investigate the reduction in belt tension and increase the belt mass.

Belt mass, is to be understood as the average minimum mass during its reasonable belt life. I suggest you to consider following possibilities, as a practical solution :

1) The material is rolling at the tripper. So, you have to reduce the inclination of tripper.

2) You have to choose new inclination and appropriate radius. The radius is to be decided considering redesigning of conveyor and drive system so that, you have the lesser tension. This you can just achieve by softer start and if need be opt for higher percentage of sag value of the belt. Here, redesigning of conveyor does not mean its replacement, but only the adjustment in certain items.

3) Based on the new profile line of the belt, you can weld bracket / pedestal on the existing tripper structure stringers, so that the belt carrying run is according to required profile. Thus, you are not wasting your existing tripper.

4) You can add a trailer of few meters length behind the present tripper as an extension of the tripper length, so that the existing tripper and the trailer fulfils the need of the revised profile of the carrying belt run.

Hope the above information will be of use to you.

Regards,

Ishwar G Mulani.

Author of Book : Engineering Science and Application Design for Belt Conveyors.

Advisor / Consultant for Bulk Material Handling System & Issues.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 25882916 ■

Greetings,

I have but one thing to add to this wonderfull topic-

"Belt training idlers at every tenth troughing idler position."

This will make your belt behave!!!!! ■